Methods of making sand cores or molds for metal casting



United States Patent 2,987,789 METHODS OF MAKING SAND CORES 0R MOLDS FOR METAL CASTING Rolf Erhard Morn, Alfredshern, Sweden, assignor to M0 Och Domsio Akfiebolag, Ornskoldsvik, Sweden, a corporation of Sweden No Drawing. Filed Aug. 11, 1958, Ser. No. 754,154 Claims priority, application Sweden Sept. 5, 1957 22 Claims. (Cl. 22-193) The present invention relates to a method of making sand molds or sand cores for metal casting and is in some measure an improvement of the so-called CO method of making molds and cores.

In the usual CO method water glass is added to the sand employed for making the molds or cores and after forming the mold or core it is treated with carbon dioxide which reacts with the water glass so that the mold or core hardens.

This method has a number of disadvantages. Above all the molds and cores manufactured by this method show an incomplete disintegration after casting which renders it difiicult to clean the castings. To improve the disintegration a number of special additives have been proposed.

The main object of the present invention is to provide a method of making molds or cores for metal casting by a technique similar to the CO method, but which produces molds and cores which disintegrate more readily after casting. Other objects and advantages will appear as the description proceeds.

According to the present invention it was found that the above-mentioned disadvantage of the normal CO, method can be removed and other advantages gained by adding to the sand an alkaline earth metal hydroxide or oxide, in particular calcium hydroxide or oxide, preferably in combination with an organic binder, and treating molds and cores produced from the sand thus obtained with carbon dioxide. It was found that the disintegration of molds and cores thus produced is completely satisfactory.

In some cases it is possible to use the alkaline earth metal hydroxide or oxide alone without adding other binders. Generally, however, a suflicient strength will not be obtained in this manner, and preferably, therefore, an organic binder is added. Examples of suitable binders are water-soluble cellulose esters and ethers, such as methylcellulose, ethylcellulose, hydroxyethylcellulose, methyl-ethylcellulose, carboxymethylcellulose, ethyl-hydroxyethylcellulose, sulfoethylcellulose, hydroxyethyl-carboxymethylcellulose, cellulose sulfate etc., sugars, starch,

dextrin and other polysaccharides, thermosetting plastics, such as phenoplastics, urea plastics, melamine plastics, if

desired combined with hardening agents, thermoplastics, such as polyvinyl chloride, and glue, natural resins, casein,

' sulfite waste liquor, core oils (drying oils) and others.

Preferred binders are water-soluble cellulo'se ethers and thermosetting plastics.

' If desired, it is possible in special cases to combine the process of this invention with the normal CO method by adding water glass, but thereby some of the advantages of the invention will be partly lost. It is also possible, in combination with alkaline earth metal hydroxide or oxide to use plaster of Paris or cement. The cement may be combined with a suitable accelerator, e.g., colcium chloride. In some cases it is possible to use the alkaline earth metal hydroxide or oxide together with other inorganic or organic bases, e.g. ammonia or monoor triethanolamine. Thereby under certain conditions an improvement of the dry strength isobtained and in addition the moisture of the sand and thus in the resulting mold or core. caube, reduced.

When the addition of alkaline earth metal hydroxide or oxide is combined with organic binders e.g. cellulose ethers, plastics or core oils, the process of this invention may be carried out so that treatment with carbon dioxide takes place until the core or mold is sufliciently hard to permit pouring. However, it is also possible to treat the mold or core with carbon dioxide only until it has suflicient firmness to be capable of being handled and then bake it in a furnace until suflicient hardness is obtained.

The amount of calcium hydroxide or oxide or other alkaline earth metal hydroxide or oxide added should be about 1 to 10% of the weight of sand while the amount of organic binder may be 0.1 to 3%. The moisture content of the sand should be 0.5 to 6%. The amount of cement or plaster of Paris, if such is used, may be 0.1 to 5%.

In addition to the abovementioned advantage of a better disintegration of the cores and molds, the process of this invention has other advantages as compared to the normal CO method. Water glass is strongly alkaline and irritates the skin as well as attacks the painting in core boxes. It is true that alkaline earth metal hydroxides are also alkaline, but they are less irritating and they do not attack the painting so strongly. Furthermore, water glass and Water-glass-containing sand have a short storage life, in that the water glass rapidly reacts with the carbon dioxide of the air. The sand mix obtained by the process of this invention is not so sensitive in this respect. Water glass is liquid, while the alkaline earth metal hydroxides and oxides can be obtained in pulverulent form and are therefore more easily measured and are more rapidly mixed with the sand. Thus, it is possible to provide a binder composition in pulverulent form comprising a mixture of alkaline earth metal hydroxide and a suitable organic binder, such as a cellulose ether, in suitable proportions to be admixed to the sand. In addition it is not necessary to work with dry sand, as is the case when water-glass is used.

When gassing the cores and molds prepared with carbon dioxide the corresponding alkaline earth metal carbonate is formed. When the metal is poured this is decomposed to form alkaline earth metal oxide and carbon dioxide. Therefore, the sand can be used again for making cores or molds after adding water and, if desired, an organic binder. Preferably, however, such return sand is mixed with fresh sand to prepare new molds or cores.

To prepare the sand mix for the manufacture of the molds or cores in accordance with this invention the alkaline earth metal hydroxide or oxide, preferably together with an organic binder, is added to dry or moist sand in a suitable mixer such as a common core or form sand mixer and sufiicient Water is added if necessary to achieve the desired moisture content as indicated above. The suitable moisture content in any specific case should be determined by preliminary tests, since it varies with the grade of sand, the working time and the specific mode of operation. It is to be understood that when an alkaline earth metal oxide is added it reacts with the water to form the corresponding hydroxide.

The normal time of blending the mix is 2 to 6 minutes depending on the efiiciency of the mixing apparatus. The mix should not be agitated so long that it becomes warm and for this reason a speed muller or an edgerunner mill is to be preferred to the types of mixers which give a high frictional heat.

The sand mix obtained in accordance with this invention will dry superficially after a few hours of storage in air. Therefore, if the sand mix is not to be used immediately it should be covered with a wet cloth or the like or the amount of water added should be slightly increased when the sand mix is prepared. A sand mix which has been dried but has not been treated with carbon dioxide can still be used if a suitable amount of water-is added thereto. The molds and cores can be produced from the-sand mix of this invention in the same manner "as from usual molding sand. When making molds it is possible to remove the pattern before treating the mold with carbon dioxide since a high green strength-is obtainable.

Treatment with carbon dioxide is preferably carried out by covering the mold flask or core box with a cover which has an inlet which can be connected to asource of carbon dioxide to blow the gas into the mold cavity or toward the core surface.

The invention is illustrated 'by'the' examples below. In examples 1-18 the sand and "the binders were blended for about /2 minute. Thereupon water-was added and the mix further blended for aboutS minutes. From the age for 1 hour, 2 hours, 4 hours and 24.hours at room temperature. an-average particle size of 0.23 mm. The calcium hy- The sand used was a core sand having droxide used was a commercial product having a Ca(OH) content of 90-95%. The amounts of binder added aregiven in percent by weight based on the dry sand.

Example 1 Binder: Calcium hydroxide 2%. -Water 3%. Green compressive strength 0.73.

Shear strength Not measurable. Compressive strength Not measurable.

Example 2 Binders:

Calcium hydroxide percent- 4 Ethyl-hydroxyethylcellulose do 04 Water 4 Green compressive strength 0.80 Sheer strength:

Immediately 0.24 1 h. 0.25 2 h. 0.26 4 h. 0.41 I 24 h. 1.45 "Compressive strength:

Immediately 0.90 1 h. 1.00 2 h. 1.00 4 h. 1.40 24h. 4.40

Example 3 Binders:

Calcium hydroxide percent 2 Ethyl-hydroxyethylcellulose do 0.4 Water do 3 'Green compressive strength 0.67

Shear strength:

Immediately 0.32 1 h. 0.13 2 h. 0.19 4 h. 0.55 24h. 1.40

4 Compressive strength:

Immediately 1.10 1 h. 0.65 2 h. 0.85 4 h. v 1.25 24 h. 2190 Example 4 Binders:

Calcium hydroxide "percent" 2 Ethyl-bydroxyethylcellillose do "0.4 Water do 3 Green compressive strength 0.85 :Shear strength:

. Immediately ee 0.29 l-h. 0.43 2 h. c 0.46

4 .h. a 0.71 24 h.. 3.20 Compressive strength: Immediately 1.50 1h. 1.90 '2 h. 2.30 4 h. 2.75 24 h. 12.40

Example 5 Binders:

Calcium hydroxide percent 2 .Ethyl-hydroxyethylcellulose .;do 0.4 Water. do 3 .Green compressive strength 1.51 .Shear strength:

Immediately 0.70 1 h. a 0.80 2 h. 0.53 4 h. 0.73 24 h. 2.70 Compressive strength:

Immediately 1133 1 h. 1.95 2 h. '1.60 4 h. 2.80 '24 h. 8.60

Example 6 Binders:

"Calcium hydroxide apercentu 2 'Carboxymethylcellulose ;do 0.4 Water cdo 3 Green compressive strength 1.97 Shear strength:

Immediately 0.40 1 h. 0.55 2 'h. 0.37 4 h. I 0.43 M '24 h. 1.80 Compressive strength:

Immediately 1.15 1 h. 1.70 2 h. 1.40 4 h. 1.60 24 h. 4.25

Example 7 :Binders:

Calcium hydroxide pereent 2 Methylcellulose do- 0.4 Water do 3 Green compressive strength 1.20

Shear strength:

Immediately 0.25 1 h. 0.35 2 0.33 4 -h. 0.45 24 h. "$52.50

Compressive strength:

Immediately 0.90 1 h. 1.40 2 h. 1.40 4 h. 2.00 24 h. 10.20

Example 8 Binders:

Calcium hydroxide percent 2 Methylcellulose do 0.4 Water o 3 Green compressive strength 1.51 Shear strength:

Immediately 0.30 1 h. 0.49 2 h. 0.53 4 h. 0.79 24 h. 3.80 Compressive strength:

Immediately 1.30 1 h. 2.20 2 h. 2.45 4 h. 3.50 24 h. 13.00

Example 9 Binders:

Calcium hydroxide percent..- 2 Hydroxyethylcellulose do 0.4 Water 3 Green compressive strength 1.03 Shear strength:

Immediately 0.50 1 h. 0.55 2 h. 0.70 4 h. 0.50 24 h. 2.50 Compressive strength:

Immediately 1.70 1 h. 1.50 2 h. 2.40 4 h. 1.70 24 h. 13.00

Example 10 Binders:

Calcium hydroxide percent 2 Sodium cellulose sulfate do 0.4 Water do"-.. 3 Green compressive strength 1.35 Shear strength:

Immediately 0.60 l h. 0.58 2h. 0.80 4h. 0.50 24 h. 2.10 Compressive strength:

Immediately 2.00 1 h. 2.20 2h. 2.70 4 h. 1.80 24 h. 6.70

Example 11 Binder: Calciumhydroxide percent 4 Water do 3 Green compressive strength 1.24 Shear strength:

' Immediately 0.58 1h. 0.75 2h. 0.85 4 h. 1.00 2411. 1.40

6 Compressive strength:

Immediately 1.60 1 h. 1.90 2 h. 2.00 4 h. 2.40 24 h. 3.40

Example 12 Binders:

Calcium hydroxide percent 4 Ethyl-hydroxyethylcellulose ....do 0.4 Water do 4 Green compressive strength 2.01 Shear strength:

Immediately 0.45 1 h. 0.75 2 h. 0.63 4 h. 0.85 24 h. 2.30 Compressive strength:

Immediately 2.00 1 h. 2.40 2 h. 2.00 4 h. 2.50 24 h. 8.20

Example 13 Binders: Calcium hydroxide percent.. 4 Carboxymethylcellulose do 0.4 Water ..do 4 Green compressive strength 2.51 Shear strength:

Immediately 0.85 l h. 1.00 2 h. 1.40 4 h. 0.78 24 h. 1.90 Compressive strength:

Immediately 3.10 l h. 3.50 2 h. 3.70 4 h. 2.70 24 h. 5.20

Example 14 Binders:

Calcium hydroxide percent 4 Methylcellulose do 0.4 Water dn 4 Green compressive strength 2.10 Shear strength:

Immediately 0.50 1 h. 0.80 2 h. 0.7 5 4 h. l 1.00 24 h. 2.90 Compressive strength:

Immediately 2.00 1 h. 3.50 2 h. 3.00 4 h. 3.30 24 h. 13.00

Example 15 Binders:

Calcium hydroxide "percent..- 4 Hydroxyethylcellulose do.. 0.4 Water do 4 Green compressive strength 1.51 Shear strength:

Immediately 1.00 l h. 0.75 2 h. 0.90 4 h. 0.75 24 h. 2.00

ames 7 Compressive strength:

Immediately 1 h. 2.00 2h 3.00 4- 2.70 24 h 9.50

Example 16 Binders: j

Calcium hydroxide. -percent 4 Sodium..cellu1ose-sulfate do 0.4 Water Green compressive strength '1- Shear strength:

Immediately 14 v V 0.40 21;, 1.30 4 h, 0.73 24 11, 1.10 Compressivestrength:

I Immediately 1.90 1h. 7 1.70 2h. 3.00 4h. 2.00 24 h. 5.50

Example 17 Binders: 7

Calcium hydroxide percent 4 Ethyl-'hydroxyethylcellulose do.. 0.8 Urea resin do 0.5 Water do 4 Greencompressive strength 2.23 Shear'strength:

Immediately 2.40 1 h. 1.65 2b. 1.45 4 h. 1.75 24h. 2.25 Compressive'strength:

Immediately 7.35 1h. 6.10 2b. 4.90 4 h. 6.35 24 h. 8.15

Example 18 Binders:

Calcium hydroxide percent-.. 8 Ethyl-hydroxyethylcellulose do 0.4 7 Mannitol jdo 0.01 Water do 6 Green compressive strength 2.50 Shear. strength:

Immediately 0.85 1 h. 0.75 24h 3.40 Compressive strength: 7

Immediately 3.00 r 24 h. 14.0

:Example .19

To investigate the risk of decrease in strength {on exicessive 'ga'ss'ing a-sand ofthefollowing composition was prepared in thesame'manneras in Examples 18.

Binders:

Calcium hydroxide ;percent Ethybhydroxyethylcellulose do 0.6 Wate'r o 4 .Green compressive strength 1.90

Test cores madeiromthis weretreated with carbon 8 dioxide under a pressure of 2 kg. per' 'sq. cmifor varying with the results indicated below:

. Compressive strength,

Time, seconds: v.kg. .per.sq.?em.

0 0.25 4 I 2.80 8 3.00 12 3.10 16 a I 3.00 20 a 3.20

Examples 20-22 below illustratethe-eifect of adding triethanolamine. The sand mixes were prepared in the same manner as in Examples 1-19. Test-cores were treated with carbon dioxide under 2 lg. per sg. cm. during 20 seconds. The green compressive strength was measured on untreated cores. The shear strength and compressive strength were measured immediately after treating with carbon dioxide and after 1 .hour,.2 hours and 24 hours storage at room temperature.

Example "20 Binders:

.Calcium hydroxide cpercentu 2 Ethyl-hydroxethylcellulose -do 1 Triethanolamine do 0 Water do 3 Green compressive strength *1 :5 8 Shear strength:

Immediately 1.15 l 0.78 2 h. 0.63 24 h. 2.25 Compressive strength:

Immediately 3.70 1 r 2.40 2 h 1.65 24h. 10.20

Example.21 Binders:

Calcium hydroxide "percent..- 2 Ethyl-hydroxyethylc-ellulose do 1 Triethanolamine do 0.1 Water 3 Green compressive strength 1.79 Shear strength:

Immediately 1.65 1 .h 1.05 2 h 0.93 24 h 3.45 Compressive strength:

Immediately 5.65 I h 4.35 2 h 3.25 24 h 12.50

Example 22 Binders:

Calciumhydroxide percent 2 Ethyl-hydroxyethylcellulose ,,dQ 1 Triethanolamine do 0.2 Water 7 7 i 3 Green compressive strength 1.73 Shear strength:

Immediately 2.00 1 h 1.40 2 h 1.25 24 h 2.45 Compressive strength:

Immediately 5.80 1.11 4.20 2h--- 3.45 24h. 12.75

'In Examples "23 32 below "the "sand "mixes-were prei l l indicated in Examples 1-18.

Example 23 Binders:

Calcium hydroxide percent.. 4 Ethyhhydroxyethylcellulose do 0.6 Molasses do 1 Plaster of Paris do 2 Water do 3 Green compressive strength 2.28

Shear strength: 7

Immediately 1.3 111 1.7 2 h 1.85 24 h 3.5

Compressive strength:

Immediately a 4.35 1 h 6.15 2 h 6.05 24 h 13.0

Example 24 Binders:

Calcium hydroxide percent- 4 Ethyl-hydroxyethylcellulose do 0.6 Molasses do 0.5

Plaster of Par do 2 Water do 3 Green compressive strength 2.55

Shear strength:

Immediately 1.6 1 h 1.65 2 h 1.75 24 h 4.05

Compressive strength:

Immediately 5.45

Example 25 Binders:

Calcium hydroxide ....percent 4 Ethyl-hydroxyethylcellulose ..do 0.6 Molasses do 1.0

Water do.. 3

Green compressive strength. 1.94

Shear strength:

Immediately 1.25 1 h 1.45 2 hr 1.65 24 h 3.0

Compressive strength:

Immediately 4.8

Example 26 Binders:

' Calcium hydroxide. ..percent.- 4 Ethyl-hydroxyethylcellulose do 0.4 Molasses do 1.0 Sulfite .waste liquor do 0.5 Plaster of Paris do.. 2 Ethanolamine do 0.1

Water 3 Green compressive strength 1.90

Shear strength:

\ Immediately 1.45 1 h. 2.05 2 h. 1.65 24 h. 3.25

I 10 Compressive strength: Immediately 4.75 1 h. 7.0 V 2 h. 6.7 5 24 h. Y 7 13.0

Example 27 Binders:

Calcium hydroxide ...percent 2 10 Ethyl-hydroxyethylcellulose ..do 0.4 Molasses do... 1.0 Water do I 2 Green compressive strength 1.22 Shear strength:

Immediately 0.88 1 h. 1.25 2 h. -1.3

24 h. 2.45 Compressive strength:

Immediately 2.95 1 h. 4.25 2 h. 3.95 24 h. 9.0

25 Example 28 Binders:

Calcium hydroxide percent 2 Ethyl-hydroxyethylcellulose do. 0.4 Molasses do 1.0 30 Plaster of Paris do 2.0 Water I do 2 Green compressive strength 1.98 Shear strength:

Immediately 1.0

1 h. 1.45 2 h. 1.5 24 h. 3.4

Compressive strength:

Immediately 5.05

-1 h. 5.0 2 h. 5.5 24 h. 11.5

Example 29 Binders:

Calcium hydroxide percent 8 Ethyl-hydroxyethylcellulose do.... 0.6 Molasses do 1.0 Plaster of Paris do 2 Water do 5 Green compressive strength 3.00 Shear strength:

Immediately 1.35 1 h. 1.8g 2 h. 2.0 24 h. 3.0

Compressive strength:

Immediately 5.5 1 h. 6.4

Example 30 Binders:

Calcium hydroxide percent 8 Ethyl-hydroxyethylcellulose do 0.6 Molasses o 0.5 Plaster of Paris, do- 2 Water do 5 Green compressive strength 3.63

Shear strength:

Immediately 1 1.35

mass '11 Compressive strength: 7

. Immediately 4.35 .1 1h." 5.9 2"h. V 5.7 24' l3.0

Example'31 Binders:

Calcium hydroxide percent 8 Ethyl-hydroxyethylcellulose do 0.6 Molasses do 1 Water do Green compressive strength. 2.23 Shear strength: J

Immediately 1.5 lb. 1.55 2 'h. V 1.45 24h. 2.85 Compressive strength:

Immediately 4.9 l 'h. 4.9 2 'h; 5.4 24-11. 10.75

Example 32 Binders:

Calcium hydroxide percent" 2 Ethylhydroxyethylcellulose ;do 0.4 Molasses o... 1.0 Portlandcement do 2.0 Water 'do ,3 Green 'compressivestrength 0.98 Shear strength:

' Immediately 0.75 1h; c r 0.95 2h; 1.25 24-h. 1.55 Compressive strength:

' Immediately 1.85 lh; 3.2 2h. 3.4

Examplejj A sand mix of the following composition was prepared in the same manner as in the examples above:

Binders: V I

Calcium hydroxide percent 1 Ethyl-hydroxyethylcellulose do 0.5

Water do '2 Cores were made from this sand mix an'dwere treated with carbon-dioxide, whereupon -they' were baked in a furnace. After treatmentwith-carbon dioxide, but before bak-ingthe cores had 'a-shearstrength ofhlkg. per sq.

cm. and after -1 hour-of-baking-at-200--C. they 'hada Binders:

Calcium hydroxide percent 2 Ethyl hydroxyethylcellulose Q. 'do 0.4 Quartz flour do 4 i Molasses "do "0.5

Water ado 3 Compressive-strength: I

' Immediately.-- 3.5 T 1b. 6.0

1'2 and the quartz "flour were ground together in a ball mill, whereupon this mixture was addedtogether with the molasses to the sand which was blended as described above.

Example 35 Binders:

Calcium hydroxide percent.- 2 Magnesiumoxide do 1 Ethyl-hydroxyethylcellulose do 0.4 Water do 2 Green compressive-strength do 1.08 Compressive strength:

Immediately 0.70 l h. 0.75 2h. 2.25

The sand mix and the test cores were prepared and treated in the same manner as in Examples 1 to 18.

I claim:

1. A binder for preparing sand mold members, based upon an alkaline earth metal carbonate as the inorganic binder, consisting essentially of an inorganic binder compound selected'from the group consisting of alkaline earth metal oxides and alkaline earth metal hydroxides andan organic binder, in the proportion of from about 1 to about 10 parts of theinorganic binder compound and from'about 0.1 to about 3 parts of the organic binder, the said' mix being capable of forming a sand mold member upon c'ombination'with sand, water and carbon dioxide.

'2. A binder mix 'inaccordance with claim 1 in which the alkaline earth metal is selected from the group consisting of calcium and magnesium.

' 3. A binder in accordance with claim' 1 in which the organic'binder is a' water-soluble cellulose derivative.

4. A binder mix in accordance with claim 1 consisting essentially of, in addition, from about 0.1 to about 5 parts of cement.

5. A binder mix in accordance with claim 3'in which the cellulose derivative'is a cellulose ether;

6. A binder mix in' accordance with claim' 3 in which the cellulose derivative isrethyl hydroxyethyl cellulose.

7., A binder mix in accordance with claim 3 in which the cellulose derivative is a cellulose ester.

.8. A binder mix'for preparing sand mold members, based upon an alkaline earth metal carbonate as the inorganic'binder, consisting essentially of sand, an inorganic binder'compound selected'irom the group'consisting of alkaline earth metal oxides and-alkaline earth metal hydroxides and an organic binder, in theproportion of from aboutl to about "10% of -theinorganic binder compound 'andfrom about"0;1'to about 3% of the organic binder by'weight 'of' the sand, the said mixbeing capable of forming asand mold 'memberupon combination with Water and carbon dioxide. V

"9. A 'binder mix for 'preparing'sand'mold members, based upon 'an alkaline earth metal carbonate as. the inorganicbinder, consisting essentially of sand, water, an inorganic binder compound selectedfromthe group consisting of alkaline earth-.metaloxides and alkalineearth metal hydroxides and an organic'binder, in the proportion of from about 1 to about 10% of the inorganic binder compound and from about.0.-1 to about 3% of the organic binderby weightofthe sand, the said being capable of forming a sand mold member upon combination with carbon dioxide.

10. A sand mold memberconsisting essentially of sand particles bonded together by a mixture, based upon an alkaline earth metal carbonate as'the inorganic binder, consisting essentially of an alkaline ,earth-metalcarbonate and an organic binderfin the proportionof from about 1 to about 10% of the carbonate and from-about l to abo.u"3'% of the'organic 'binder'by weight of the,.sand.

'11. A sand mold member in accordance with claim 10 in which the organic 'bin'deris a water-soluble cellulose The 'calciumhydroxide, the 'ethyl hydroxyethylcellulose derivative.

12. A method of making sand mold members bonded together by a binder based upon an alkaline earth metal carbonate as the inorganic binder, for use for metal castings which comprises forming into the desired mold shape a mix consisting essentially of sand, water and from about 1 to about 10% by weight of the sand of an inorganic binder compound selected from the group consisting of alkaline earth metal oxides and alkaline earth metal hydroxides, and reacting said binder compound with carbon dioxide under reaction conditions to form an alkaline earth metal carbonate in situ in an amount sutficient to bind the sand and form the mold member.

13. A process in accordance with claim 12 in which the binder mix comprises an organic binder, in an amount from about 0.1 to about 3% by weight of the sand.

14. A process in accordance with claim 12 in which the inorganic binder is calcium oxide.

15. A process in accordance with claim 12 in which the inorganic binder is calcium hydroxide.

16. A process in accordance with claim 12 in which the inorganic binder is a mixture of calcium hydroxide and magnesium oxide.

17. A process in accordance with claim 12 in which the mix consists essentially of, in addition, from about 0.1 to 5% cement by weight of the sand.

References Cited in the file of this patent UNITED STATES PATENTS 575,074 Smith Jan. 12, 1897 1,909,008 Prange May 16, 1933 2,383,812 Navias Aug. 28, 1945 2,883,723 Moore Apr. 28, 1959 FOREIGN PATENTS 986,904- France Apr. 11, 1951 710,099 Great Britain Apr. 1, 1952 158,812 Australia Nov. 28, 1952 531,968 Canada Oct. 16, 1956 

12. A METHOD OF MAKING SAND MOLD MEMBERS BONDED TOGETHER BY A BINDER BASED UPON AN ALKALINE EARTH METAL CARBONATE AS THE INORGANIC BINDER, FOR USE FOR METAL CASTINGS WHICH COMPRISES FORMING INTO THE DESIRED MOLD SHAPE A MIX CONSISTING ESSENTIALLY OF SAND, WATER AND FROM ABOUT 1 TO ABOUT 10% BY WEIGHT OF THE SAND OF AN INORGANIC BINDER COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALINE EARTH METAL OXIDES AND ALKALINE EARTH METAL HYDROXIDES, AND REACTING SAID BINDER COMPOUND WITH CARBON DIOXIDE UNDER REACTION CONDITIONS TO FORM AN ALKALINE EARTH METAL CARBONATE IN SITU IN AN AMOUNT SUFFICIENT TO BIND THE SAND AND FORM THE MOLD MEMBER. 